Geometric action of an arbitrary orthogonal 3x3 matrix with determinant -1

In summary, the conversation discusses two proposed solutions for describing the geometric action of an orthogonal 3x3 matrix with determinant -1. The first solution describes it as an improper rotation, while the second solution involves a rotation followed by inversion through the origin. The conversation also mentions a preference for the second solution as it explicitly mentions rotation about the origin.
  • #1
kalish1
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Hi,
I have a question about describing geometrically the action of an arbitrary orthogonal 3x3 matrix with determinant -1. I would like to know if my proposed solutions are satisfactory, or if they lack justification. I have two alternate solutions, but have little confidence in their validity. Any help would be greatly appreciated!

Solution 1: The orthogonal 3 x 3 matrix with determinant −1 is an improper rotation, meaning it is a reflection combined with a proper rotation. In another sense, an improper rotation is an indirect isometry, which is an affine transformation with an orthogonal matrix with a determinant −1.

Solution 2: A rotation about the origin, followed by inversion through the origin (i.e. (x,y,z)-->(-x,-y,-z) ). Note that a "left-handed object" turns into a "right handed object", so "handedness is reversed" but otherwise it is just like a rotation.

Thanks in advance!
 
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  • #2
Your "solution 1" does not say "rotation about the origin" so "solution 2" is better. Other than that, they both say the same thing.
 

FAQ: Geometric action of an arbitrary orthogonal 3x3 matrix with determinant -1

What is a geometric action of a matrix?

A geometric action of a matrix refers to the transformation of a geometric object, such as a point or a vector, when it is multiplied by the matrix. This transformation can include rotations, reflections, and translations.

What is an arbitrary orthogonal 3x3 matrix?

An arbitrary orthogonal 3x3 matrix is a square matrix with three rows and three columns whose columns and rows are all orthogonal to each other. This means that the dot product of any two columns or rows of the matrix is equal to zero. Additionally, each column and row has a length of 1, making it an orthogonal matrix.

What does it mean for a matrix to have a determinant of -1?

The determinant of a matrix is a scalar value that represents the scaling factor of the matrix transformation. A determinant of -1 indicates that the matrix is a reflection matrix, which means it flips the orientation of the object it is applied to.

How does a matrix with a determinant of -1 affect the geometric object it is applied to?

A matrix with a determinant of -1 will cause a reflection or a rotation of the object it is applied to. The exact transformation will depend on the specific values of the matrix elements, but it will always result in a change in the orientation of the object.

Can an arbitrary orthogonal 3x3 matrix with a determinant of -1 have other geometric actions?

Yes, an arbitrary orthogonal 3x3 matrix with a determinant of -1 can also have translations and rotations, as long as it maintains its orthogonal properties. However, the reflection action will always be present due to the determinant being -1.

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